Antiplatelet Drugs

May 19, 2006 12:00 am

Drugs that reduce the formation or inhibit the action of chemicals that promote the activation and aggregation of platelets, blood components important for the clotting of blood. Although clotting is an important step in wound healing, inappropriate clotting can be harmful. The most familiar and most used antiplatelet drug is aspirin. Other members of this family of drugs include abciximab (brand name Reopro), clopidogrel (Plavix), dipyridamole (Persantine), eptifibatide (Integrilin), ticlopidine (Ticlid), and tirofiban (Aggrastat). They are used to treat and prevent cardiovascular disease; to treat angina (chest pain), some strokes, and transient ischemic attacks (ministrokes); to prevent clot formation in people with atrial fibrillation (irregular heartbeat); and to prevent blood vessels and grafts from closing up after angioplasty and heart bypass surgery.

As platelets circulate through the bloodstream, they’re constantly sensing and measuring the levels of certain signaling molecules. Normally, the balance of chemical signals keeps platelets in an inert state. When the level of chemicals calling for activation outweighs the level of chemicals promoting their free circulation—such as occurs near the site of a break in a blood vessel—platelet activation occurs. Once activated, platelets change their outer membranes, clump together at the site of the injury, and release chemicals that promote further platelet aggregation. People with diabetes tend to have hyperactive platelets that are more likely to form clots.

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Users of antiplatelet drugs are at increased risk for bleeding problems such as hemorrhagic stroke and gastrointestinal bleeding and are also at risk for neutropenia (having an abnormally small number of a type of an infection-fighting white blood cell). Some of these medicines can cause significant sodium retention, so if you take one, your doctor may have you work with a dietitian to reduce or even eliminate sodium from your diet.

In addition to taking part in wound healing, platelets also have a role in the progression of atherosclerosis, a disease of artery narrowing. In atherosclerosis, fat, cholesterol, platelets, and calcium are deposited on the walls of blood vessels whose linings have been damaged. (Blood vessel damage is caused by factors such as high blood pressure, diabetes, and smoking.) These deposits, or plaques, gradually narrow the blood vessel and reduce the flow of blood through it. Depending on the location of a plaque, reduced blood and oxygen flow can cause symptoms such as angina or claudication (pain in the legs that starts when walking but eases with rest). If part of a plaque ruptures and breaks free, it can travel through the circulatory system and block off a blood vessel, causing problems such as stroke or a heart attack.

Studies have shown, though, that aspirin can be used as a preventive measure that reduces the incidence of strokes by 20% and heart attacks by about 30%. These reductions are not insignificant when you consider that cardiovascular diseases are the leading cause of death for people with diabetes and that people with diabetes are at higher risk for cardiovascular diseases.

The American Diabetes Association (ADA) recommends aspirin therapy (the use of a daily aspirin as preventive medicine) for adults with diabetes who have increased risks for cardiovascular diseases. That group includes people over 40, smokers, people with high blood pressure, people with a family history of cardiovascular disease, people who have high cholesterol levels, and people who have protein in the urine (albuminuria). Aspirin therapy is not recommended for people under 21 because its use increases the risk of Reye syndrome.

Because higher doses of aspirin may increase the risk of side effects without an increase in cardiovascular benefits, the ADA and the American Heart Association recommend that people with cardiovascular risk factors use low doses (75–160 mg) of aspirin. Despite its name, enteric-coated aspirin does not appear to help reduce the risk of gastrointestinal bleeding. People who are aspirin-intolerant may gain similar cardiovascular benefits from using clopidogrel instead of aspirin.

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